1. Field of the Invention
This invention relates to machines for shot peening workpieces and, more particularly, to machines for subjecting workpieces to stress peening processes. "Stress peening" refers to the operation of shot peening a part while it is statically stressed in the same direction as the stress which is to be sustained when the part is in service. Still more specifically, the present invention relates to machines for stress peening workpieces of the leaf spring type such as are currently employed in automotive vehicle suspension systems.
2. Description of the Prior Art
Leaf springs are conventionally fabricated by hot rolling or otherwise shaping spring steel or other spring material into the required shape. The ends of the blanks are then curled to form eyes for receiving the mounting shackle bolts. The blades are then heat treated to hardening temperature and then quenched and tempered. It has been determined that if the spring blade is now shot peened while under load, it will possess improved strength and life characteristics, whereby for a given weight suspension problem a spring of reduced size and weight may be successfully employed. The advantage of stress peening of leaf springs is well known in the art.
Various stress peening machines have been disclosed such as that shown in U.S. Pat. No. 3,131,457 dated May 5, 1964 to W. L. Correll et al. This patent discloses a stress peening machine which uses a large ram to deflect the spring while it is carried into the range of the shot peening equipment. A machine of this type is exceedingly complicated and expensive to manufacture. The stress peening machine of the present invention not only is much less complicated and cheaper to build but it can stress peen more springs in a given time than that shown in U.S. Pat. No. 3,131,457.
The testing device shown in U.S. Pat. No. 2,835,129 dated May 20, 1958 to G. C. Reiser et al. also shows a machine which can deflect springs using a hydraulic ram. This machine is not well suited to the high output requirement for the manufacture of automotive leaf springs.